This invention relates generally to protective boots for automobile components, and particularly to a protective boot for a constant velocity joint.
Blow molding is a well-known technique used for manufacturing hollow plastic protective boots for automobile components. However, such boots typically have a complex shape which can present difficulties to blow molding such an article.
Protective boots used on automobile components, such as a boot for a constant velocity joint (CVJ), perform several functions including protecting the joint from outside dirt and debris, as well as maintaining lubricant around the joint. Many protective boots, however, must attach to automotive components which do not have a cylindrical external configuration to which the boot may be clamped. For example, due to the bearing configuration of typical constant velocity joints, the shaft to which one end of a CVJ boot must clamp is lobed, rather than cylindrical. Thus, in order to perform its protective functions properly, a CVJ boot requires a seal or bushing element at one end to be clamped between the boot and the shaft. The bushing has a tri-lobed internal configuration.
In use, however, the addition of this extra element increases the ways in which the protective boot may fail. For example, if there is an incomplete seal between the bushing and the boot, lubricant may be allowed to escape from the joint or contaminants allowed to enter.
Accordingly, there is a need for a single piece boot and bushing which provides a suitable external clamping surface and an internal irregular surface which can be configured to meet the requirements of a mechanical structure in association with which the product is to be used. Producing such a product is very difficult using conventional blow molding techniques. Conventional blow molding techniques cannot be used to comprise a lobed internal surface on a portion having a cylindrical outer surface because thermoplastic material spreads out evenly under the effect of blowing pressure in typical blow molding.
A technique which overcomes this problem is disclosed in the applicant""s co-pending U.S. Pat. Application Ser. No. 08/694,234, filed Aug. 8, 1996, now U.S. Pat. No. 5,900,205, which is incorporated herein by reference. That application discloses a combined blow molding and compression molding technique in which a parison is confined in a mold and, prior to blowing, a core is introduced into the mold to move thermoplastic material axially, radially and circumferentially to form an integral boot and lobed bushing product. The method disclosed in that application has the limitation, however, that only a certain amount of thermoplastic material may be. moved by the introduction of a core or slides into a mold prior to blow molding, thus limiting the size of lobes which may be formed on a bushing portion of an integral bushing and boot.
Accordingly, there is a need for a process which is capable of molding an integral thermoplastic boot and bushing having unlimited lobe size or having other non-cylindrical internal surface.
The present invention provides an improved protective boot for an automotive component and a method of making. In one aspect the invention provides a thermoplastic protective boot for an automotive component having an integral bushing, comprising:
a boot element, the boot element having a first portion with a generally cylindrical outer surface for engaging with a circular clamp; and
a bushing element, the bushing element having a generally cylindrical wall portion and a plurality of lobed portions, the wall portion having a thickness, the lobed portions projecting inwardly from the wall portion a distance of at least four (4) times the thickness of the wall portion.
In another aspect the invention provides a protective boot assembly for an automobile component comprising:
a generally tubular body having first and second open ends, the body having a flexible bellows-shaped portion intermediate the first and second ends, the first end comprising a skirt portion, the skirt portion being defined by a generally cylindrical first wall, the first wall having inner and outer surfaces, the outer surface being generally cylindrical for engaging a circular clamp, the outer surface having a plurality of projections projecting outwardly from the first wall at the first end for retaining a circular clamp, the boot having one or more projections projecting inwardly of the first wall, the second end comprising a neck portion, the neck portion being defined by a generally cylindrical second wall, the second wall having a generally cylindrical outer surface for engaging a circular clamp, the outer surface having a plurality of projections projecting outwardly from the second wall at the second end for retaining a circular clamp; and
two circular clamps, wherein one of the clamps is located around the boot at the skirt portion and one of the clamps is located around the boot at the neck portion and the clamps are retained in place by the projections.
In a third aspect the invention provides a method of producing a thermoplastic protective boot for an automotive component having an integral bushing comprising:
forming a boot element having a first portion, the first portion having a generally cylindrical first wall with an inner and outer surface, the first wall having a first diameter at the inner surface;
forming a bushing element having a generally cylindrical second wall with an inner and outer surface, the second wall having a second diameter at the outer surface, the second diameter being approximately equal to the first diameter of the boot element, the inner surface of the bushing element having one or more projections inwardly of the second wall;
positioning the bushing element within the boot element so that the outer surface of the bushing element is substantially in contact with the inner surface of the boot element; and
integrating the boot element and the bushing element by thermally fusing the elements together.